Various techniques for defrosting refrigeration systems are known. For example, a common method for defrosting a refrigeration system is to stop the refrigeration cycle and activate heaters placed near the evaporator coils. These heaters defrost and deice the evaporator coil. This method, however, is time consuming and often causes undesirable heating of the refrigerated area. Another method for defrosting refrigeration systems is to reverse the refrigeration cycle. When the refrigeration cycle is reversed, hot refrigerant vapor from the compressor is directed into the evaporator outlet, through the evaporator, into the condenser inlet, through the condenser, and back into the compressor. A problem with this method is that often the temperature of refrigerant entering the compressor is so low that some liquid is introduced into the compressor. This liquid may damage or destroy the compressor. In addition, the temperature of the refrigerant entering the evaporator is often too low for rapid or complete defrosting of the evaporator. Thus, the defrost cycle may be very time consuming or the evaporator may not be completely defrosted.
A conventional refrigeration defrost system is shown in U.S. Pat. No. 4,102,151 issued to Kramer, et al. The Kramer patent discloses a hot gas defrost system in which superheated refrigerant vapor from the compressor is routed through a tank filled with water. The superheated refrigerant vapor heats the water in the tank to a high temperature. The hot refrigerant then traverses the evaporator to defrost the evaporator coil. The refrigerant exiting the evaporator is then routed through the tank containing the hot water to reheat the refrigerant and ensure that all the refrigerant is in vapor form. The vapor refrigerant then enters the compressor to complete the defrost cycle. This defrost system requires a complex system of pipes, valves and a large water tank.
A conventional refrigeration defrost system is also shown in U.S. Pat. No. 5,056,327 issued to Lammert. The Lammert patent discloses a hot gas defrost system in which, during the defrost cycle, a series of valves and pipes are used to direct the refrigerant through the compressor, evaporator, condenser and back to the compressor, thereby utilizing the condenser as a reevaporator during the defrost cycle. The Lammert patent also discloses a superheater in a defrost passage which receives refrigerant from the condenser outlet during the defrost cycle and delivers it to the compressor inlet. Additionally, the Lammert patent discloses a passage, which connects the compressor outlet and the evaporator inlet, that is, in a heat exchange relationship with the superheater in the defrost passage. The superheater allows heat from the hot vapor refrigerant discharged from the compressor to be used to heat the refrigerant delivered to the compressor inlet. This refrigeration defrost system undesirably requires numerous valves, pipes and a superheater to appropriately route the refrigerant during the defrost cycle.
Another conventional refrigeration system is disclosed in U.S. Pat. No. 5,050,400 also issued to Lammert. This Lammert patent discloses a refrigeration system including a series of valves and interconnecting fluid passages which allow refrigerant to flow sequentially from the compressor to the evaporator and, via a defrost passage, to the condenser and back to the compressor during the defrost cycle. This system includes a combined superheater/receiver located in the defrost passage for use during the defrost cycle. The combined superheater/receiver includes an inlet for receiving refrigerant from the condenser during the refrigeration cycle, a first outlet for delivering liquid refrigerant to the evaporator during the refrigeration cycle, and a second outlet for delivering refrigerant vapor to the compressor during the defrost cycle. During the defrost cycle, the system also employs a closed fluid conduit which uses the hot vapor refrigerant discharged from the compressor to heat the refrigerant entering the compressor. This closed fluid conduit ensures that all the refrigerant entering the compressor is in vapor form. Undesirably, this refrigeration defrost system requires extensive hardware, including numerous pipes and valves, to accomplish the appropriate routing of the refrigerant during the defrost cycle. This refrigeration system also requires the use of a superheater/receiver which adds to the complexity and cost of the system.